In skin treatment, generally speaking, a skin treatment device contains an active component that acts on the skin. This component, in operation, performs an action on the skin that constitutes the actual treatment. The action may be mechanical, such as for instance in the case of shaving devices, depilation devices, abrasion devices etc. The action may be thermal, such as for instance in the case of optical epilation devices where a laser beam is applied to the skin in order to destroy part of the hair follicles. In the case of optical epilation devices, the prior art comprises flash-type embodiments that generate one light flash or a limited number of flashes, and the user is supposed to hold the device steady during flashing and to displace the device in between flashing. In contrast thereto, the present invention relates to continuously operating devices that need to be displaced continuously. It is noted in this respect that “continuously operating” includes the situation where a device is continuously generating light flashes, so that the device is to be displaced while flashing. In most, if not all, cases where the device is to be displaced over the skin whilst being in operation, optimum results require an optimum displacement speed. It will easily be understood that too high a speed will result in inadequate treatment results, while the user can do damage to his skin if the device is displaced too slowly or, worse, is held still.
It is true that the user manual may inform the user of the optimum speed or optimum speed range, in centimeters per second, but a problem for the user is how to determine that he is actually displacing the device at the right speed. In practice, this means that users have to go through a lengthy learning process before they have developed a “feeling” of correct speed and before they are able to apply the correct speed consistently.
To reduce this problem, solutions have already been proposed where the device is provided with a speed sensor for detecting the relative speed between the device and the skin, and where the device is provided with an indicator giving the user feedback information. However, the prior art solutions have been found to be unsatisfying.
The indicator may give a sound signal. However, it was found that for the average user it is quite difficult to interpret sound signals.
The indicator may give a tactile signal, such as vibrations. However, apart from the disadvantage that the vibrations are inconvenient to the user, it was found that for the average user it is quite difficult to interpret tactile signals.
US-2007/0129771 discloses a device where the indicator gives an optical signal. Different colours are used to indicate “too high”, “too low”, or “within range”. This has disadvantages in that the system is not intuitive, it requires the user to learn which colour has which meaning, and the information given to the user is very coarse.